I've just recently gotten back into photography after a number of years where I slowly devolved to an iphone shooter. While the weather was clear in December I started trying to do some astrophotography with my e-m1 ii. The simple stuff, single frame or stacked frame with exposures in the 10-20 second range. I read what I could find online, did the iso invariance test and concluded that in low light noise reached a minimum at 800 or 1600 iso with my camera. 1600 seemed to have slightly less noise and 800 seemed to retain detail slightly better, but really it was a wash as far as my eyes could tell. I decided to shoot as iso 800 under the logic that I would minimize overexposure and cooresponding CA around really bright stars. Seems to work, I didn't get an amazing shots, but I definitely got some good ones. Getting to the point..... Looking at other peoples m43 images I see a wide range of iso being used from 800 all the way up to 12,800. If my understanding of how iso works is correct there's no extra signal in higher iso shots just amplification of the same signal. This amplification can be employed in pp as well with, I reason, better control over highlights as so forth. Am I missing something? So what iso do you shoot at and why?